The invention relates to a process for the production of structures by the polymerization or depolymerization of resist layers.
The term resist is defined herein as a substance capable of being applied to the surface of a substrate in order to mask the area the substance covers, i.e., to protect the substrate against the attack of, for example, etching agents, chemical or galvanic metallizing baths, or the like. Resists, such as photosensitive resists, have the property that their solubility varies under exposure to UV, electron, x-ray or ionic radiation. During exposure, either polymers are formed and cross-linked (so-called negative layers) or existing polymers are fragmented and converted into low molecular weight, soluble compounds (so-called positive layers). The property of solubility variation in the exposed, or unexposed surface areas, respectively, is utilized to produce a washout relief on the surface of the substrate by means of subsequent chemical development process.
The increasing integration density of integrated circuits requires ever-higher resolutions and lower dimensional tolerances as the field size of the structural image increases. In order to satisfy these requirements, in addition to the standard process of lithography and UV exposure, novel processes with electron beams, x-rays and ion beams are being developed. However, the smaller structural widths in the resist layers, made possible by these new processes, are attained at the price of certain, in part severe, disadvantages.
Exposure with electron radiation, using a beam directly scribing the structures, for example, has the advantage of a high resolution and low field distortion. This process is still not economical in view of the very long exposure times required. A 4" wafer may be exposed with UV radiation within a few seconds, whereas electron beam exposures usually require several tens of minutes. By projecting a mask with electron beams, shorter exposure times of approximately 2-3 minutes are obtained; however, the highest resolution is not achieved. There is also the disadvantage that expensive special electron beam masks are required.
Even x-ray lithography requires long exposure times of up to 15 minutes per 4" wafer. Furthermore, only proximity projection methods are possible in this case, and present extreme demands on the 1:1 masks used.